Apparatus for tube bending



Nov. 30, 1943. v Ns o 2,335,342

APPARATUS FOR'TUBEZBENDING, I

Filed April 28, 1941 s Sheets-Sheet 1 A. 'r. KVAR'NSTROM APPARATUS FOR TUBE BENDING Filed April 28' Nov. 30, 1943.

, 1941 s Sheets-Sheet 2 flifred Iii/urns in mime- 18.

Nov. 30, 1943. A. T. KVARNSTROM 2,335,342

APPARATUS FOR TUBE BENDING Filed April 28, 1941 3 Sheets-Sheet 3 III M Patented Nov. 30, 1943 I APPARATUS FOR TUBE BENDING Alfred '1. Kvarnstrom, Detroit, Mich, assignor to Bundy Tubing Company, Detroit, Mich, a corporation of Michigan Application April 28, 1941, Serial No. 390,694

1 Claim.

This invention relates to tube bending, and particularly-to apparatus for bending tube.

When a straight length of tube is bent on a radius, it is obvious that there must be some displacement of metal, since the portion of the tube wall on the outside of the bend, and therefore on a greater radius, is relatively long while the portion of the tube wall on the inside of the bend is relatively short. Heretofore, this displacement of metal has resulted in a thinning of the metal on the greater radius, thus weakening the wall structure. Furthermore, if the bend is on a relatively short radius, the wall on the outer portion of the bend is liable to be collapsed or partially collapsed, thus restricting the tube.

The present invention aims to provide improvements in tube bending wherein the outer wall is different directions without employing an in-- ternal supporting arbor and wherein the lash ioned tube may be easily and quickly released from the bending apparatus. The invention also provides an arrangement by means of which the tube wall can be expanded so as to form an en- Fig. 9 is a plan view of the modified form of bending apparatus.

Fig; 10 is a cross sectional view taken substantially on line llll0 of Fig. 9 showing the die.

Fig. 11 is a view illustrating means for operating a sizing punch.

The die illustrated in Figs. 1 to 6, inclusive, as illustrated in Fig. 6, may comprise two die blocks, one of which is shown at l and the other at 2 arranged so that they can be separated. To this end the block i may be fixedly mounted on the ends of rods 3 while the die block 2 may slide thereon, so that the die may be opened and closed by any suitable means. The die blocks may be .guided together and accurately positioned by dowel pins 4. The die blocks have grooves therein arranged to be matched to thus provide a channel or guldeway which substantially fits the tube. The die block i, in the form shown in Figs. 1 to 6 inclusive, has a groove 6 which is generally of U formation while the block V 2 has a groove 7, and when the die blocks are largement in an intermediate portion of a length of tube, and this without the employment of an internal arbor or expanding device.

The invention is exemplified in the accompanying drawings wherein two different forms of devices are shown for bending or fashioning tube. In these drawings Fig. 1 is a view showing a die block with a straight length of tube therein ready to be bent.

Fig. 2 is a view similar to Fig. 1 showing the tube partially bent.

Fig. 3 is a view similar to Figs. 1 and 2 showing a. further advanced step in the bending of the tube.

placed together the grooves form a closed U- shaped channel.

There are two punches or plungers respectively illustrated at I 0 and l I, and they may be carried by a single supporting head l2. One of the plungers, such as the plunger I0, is arranged to force or pusha length of tube along the die channel, and to this end it may have a reduced end portion 13 so that its shoulder It may engage the end of the tube with the reduced portion It extending into the tube. The punch or plunger It performs a shaping and sizing operation, and it has a reduced end 15 terminating at a shoulder I6. The end 15 is preferably longer than The operation of this apparatus and the method are as follows: A length of tube, as 11- lustrated at 20, is pushed into the channel of the die. and suitable means may be provided for adfvancing theholder l2 relative to the die blocks.

As the plungers advance, the tube is. forced to follow the channel formation intthe die blocks structure shown in Figs. 1 to 6. As the leading end of the tube passes through the curved formation, its end is slightly deformed. For example, the inner wall at the bend may project away from th wall of the channel as illustrated at 2|, while the opening at the leading end may not be in the form of a true circle or symmetrical. The point I! is positioned to enter the end of the advancing tube, to which end the point I1 is properly positioned, and the surface I9 adjacent the end connects the shape of the portion 2| as illustrated in Fig. 3. Continued movement causes the reduced end IE to enter the leading end of the tube until the Fig. 5 position is reached, at which time the shoulders l4 and I6 abut ends of the tube and may subject the tube structure to compressive forces. These compressive forces are not for the purpose of upsetting the metal, but may be suflicient to give the tube its final set and shape. In this final position, as shown in Fig. 5, the curved surface [8 substantially parallels for a distance the outer surface of the U- shaped channel so that this leadingsection of the tube is ironed out against the walls of the channel.

A sizing punch 31 is arranged to enter the leading end of the tube, and to this end it may have a reciprocatory movement given to it by suitable means such as a closedcam 38, the die being mounted on 'a slidable head 39 The two die blocks may be mounted upon a base 40, and one of the blocks may be arranged-for lateral move ment to open the die. To this end the block 35 (Fig. 10) may be shifted to a position as indicated by the dotted line position sothat when the die blocks open the fashioned tube may fall through an opening II in the base. The operation is substantially the same as the operation of the form above described, in that the plunger 32 forces the tubethrough the forming channel portion of the die and at the end of the die blocks with a suitable enlarged portion as il- By this arrangement a length of tube can be fashioned or bent on a very short radius as regards the diameter of the tube. For example, a tube fashioned from strip steel stock having an outside diameter of about .375 of an'inch and a wall thickness of about .028 of an inch can very readily be bent through 180 on a radius of an inch. In other words,'the distance across the diameter of the bend measured from center to center is 1 inch. Yet the bending of the tube on such a short radius does not collapse the tube wall not reduce the thickness of the wall section on the outside of the bend to any appreciable extent. To the contrary, the wall at the inside of 5 the bend is thickened by the flow of metal. This lustrated at 42. The compressive forces which are applied to the tube at the end of the bending operation forces the wall of the tube outwardly against the walls of the enlarged portion to thus expand the same. I a

I claim:

An apparatus for making a U bend in a length of tube which comprises, an openable die block having an unobstructed U shapedv die passage therein with the ends of the legs of the passage is illustrated in several of the views where it will ration as illustrated at 36 on the center line of.

the tube. These die blocks are arranged to give the tube a multiple or compound bend. As shown in Fig. 8 the leading end is bent upwardly as Fig. 8 is viewed, while in Fig.9 the tube is bent laterally.

:op'ening through one side of the die block, a

to advance into the other leg of the U-shaped I passage to substantially straighten the same whereby the tube is fashioned into U shape, an-

other plunger having an end portion for entering the leading end of thetube to expand the tube end against the wall of the die passage to reshape and correct distortions therein caused by its passage through the'bight portion of the diepassage, and shoulders on the two plungers of a size as to pass into the die passage for engaging both the trailing and leading ends of the tube to apply compressive forces thereto after the same have been shaped.

, ALFRED T. KVARNSTROM. 

